Since the invention of the telephone, it has been possible for individuals to verbally communicate with each other without being physically located in the same place. More recently, voice and video conferencing systems have allowed groups of individuals to interact with each other as if they were sitting around the same table even though they may be half way around the world.
In order to enable multiple audio sources, such as multiple people speaking, to be heard at the same time, such conferencing systems frequently contain mixers to mix the audio signals. These mixers typically receive several input signals, select a subset of those signals as being active, e.g., based on amplitude, and then mix the active signals together.
Mixers are typically limited in how many input signals they can receive, however. In order to overcome this problem, prior systems have cascaded mixers so that an output of one mixer is feeding the input of another. In this way, a single input of a mixer can be used to receive multiple input signals that have already been mixed together from another mixer.
Similarly, video composers have combined video signals in an analogous fashion.
FIG. 1 is an illustration of such an arrangement of mixers. As shown, the arrangement may include three mixers 10, 20, and 30. Each of these mixers may include an input section 14, 24, and 34 and a mixing section 15, 25, and 35. One mixer, here mixer 10, is the master mixer and the other mixers, here mixers 20 and 30, are the slave mixers with their outputs connected to inputs of mixer 10. As also shown in FIG. 1, three participants 11, 12, and 13 are illustrated as being connected to mixer 10, three participants 21, 22, and 23 are illustrated as being connected to mixer 20, and three participants 31, 32, and 33 are illustrated as being connected to mixer 30.
As shown, each of the participants 11, 12, 13, 21, 22, 23, 31, 32, and 33 receives an output signal from a mixing section of one of mixers 10, 20, and 30. These output signals are a combination of the signals from the local mixer (e.g., mixer 10 for participants 11, 12, and 13) as well as remote mixers (e.g., mixers 20 and 30 for participants 11, 12, and 13).
In order to provide this combination of signals, the input sections of mixers 10, 20, and 30 first select a subset of their inputs for mixing. For example, the input section of mixer 10 will compare the signals from participants 11, 12, and 13 and the outputs of mixers 20 and 30 to identify a subset of signals to be mixed. This signals could be four signals from participants 11 and 12 and mixers 20 and 30, as a more particular example. The mixing sections of the mixers then combine the selected signals and produce an output to be provided to the local participants and other mixers.
Because at least one output of each mixer 10, 20, and 30 is connected to an input of another mixer, the input from each participant can propagate to all participants through the other mixers. For example, assume participant 31 is speaking loudly enough to be selected by input section 34 of mixer 30. The signal from that participant would be selected and mixed with some other set of signals (e.g., one or more of participants 32 and 33 and/or the output signal from mixer 10) and output to participants 31, 32, and 33 and mixer 10. Mixer 10 would then select and mix signals from participants 11, 12, and 13 and mixers 20 and 30. Again, assuming that the signal from participant 31 is suitably loud, the signal from participant 31 would then be included in the output of mixer 10. Mixer 20 would then receive the output signal of mixer 10, compare it to the signals from participants 21, 22, and 23, select some set of these signals, mix the set of signals, and then output the mixed signal to participants 21, 22, and 23 and mixer 10. Thus, the signal from participant 31 would propagate through mixer 30 to mixer 10 and then to mixer 20, and then to participant 21 (for example).
This approach to mixing signals is problematic, however, in that it increases delay, accumulates signal quality degradation, and limits audio mixing capabilities. For example, because an input signal originating at a slave mixer needs to travel through that slave mixer and the master mixer in order to arrive at another slave mixer, there is increased delay over a configuration in which the two slave mixers were connected directly, for example. Similarly, as another example, this routing of the input signal also accumulates signal quality degradation because each mixer introduces its own signal degradation. And, because each mixer selects and produces a mixed signal that cannot be separated based upon its own inputs, audio mixing capabilities by the other mixers are limited to what signals are chosen to generate the mixed signal.
Likewise, combining of video signals in a similar fashion is also problematic.
Accordingly, improved methods, systems, and media for mixing conferencing signals are desired.